Expansion of Field Margin Size Mitigate the Hazard of Rotary Tillage to Earthworm in Rice-Rape Rotation System

Abstract

Field margin (FM) provides refuges for earthworm survival in rape-rice system after flooding, while the effects of FM with different size on earthworm in arable field (AF) is unclear. In this study, we investigated the effects of different FM sizes, a conventional size (FM I) and three expanding sizes (FM II, FM III, FM IV), on earthworm population characteristics in FM and AF. The results showed that the mean abundance of earthworm under the expanding sizes at 1 day and 60 day of flooding after rape harvest was 16.5 and 20.2 times higher than that of FM I, respectively. After stopping flooding, juveniles first migrated from FM to AF, whereas more than half of them were killed by subsequent rotary tillage, and the mortality decreased with expanding FM size. Subsequently, expanding FM sizes promoted earthworm to distribute evenly through the AF at faster speeds. At rape maturity, the mean abundance and total biomass of earthworm of AF under expanding FM sizes were significantly greater than that of FM I, and this positive effect increased with expanding FM size. The results indicated that expanding FM size can mitigate the hazard of rotary tillage to earthworm and promote rapid recovery of earthworm population in AF.